Table 2. — Lengths of mid juvenile fall chinook salmon from 

 the Snake River during migration past sampling site, 

 1963-64 



Length of fish at stage of migration 

 Year Early > Late 2 



Fisli Mean Range Fisli Mean Range 



Number Mm. Mm. Number Mm. Mm. 



1962 76 62 33-80 434 71 47-103 



1963 - -... 97 73 48-99 133 81 67-98 



1964 (») - 146 79 61-90 



' Mid-April to mid-May. 



2 Mid-May to mid-June. 



3 No discernible fish of this group in sample. 



1964 and 1965, bhe two populations were separated 

 by the percentajie of each age group in the daily 

 sample as estimated from scale analysis. 



The average length of spring chinook salmon 

 varied from 106 mm. in 1962 to 149 mm. in 1964 

 (table 3). Each year the average size increased 

 from the beginning to the end of the migration. 



A few large individuals (215-260 mm.) were 

 captured in 1963 and 1964, but the total constituted 

 less than 1 percent of the catch. These fish (age- 

 group III) appeared at the trap early in the season 

 during extremely high flows from the Weiser 

 River. 



Table 3. — Lengths of juvenile spring chinook salmon from 

 the Weiser River during migration past sampling site in 

 the Snake River, 1962-65 



Length of fish at stage of migration 

 Year Early ' Late 2 



Fish Mean Range Fish Mean Range 



Number Mm. Mm. Number Mm. Mm. 



1962 8 106 95-117 104 134 125-161 



1963 438 108 94-140 62 142 116-165 



19&4 249 112 100-146 81 149 126-166 



1966 19 119 101-130 22 140 120-165 



1 April to pealc of migration (late April or early May). 



2 From peak of migration through May. 



Eagle Creek population. — Juvenile spring chi- 

 nook salmon from Eagle Creek migrated down- 

 stream most of the year except during the summer 

 when flows averaged less than 1 c.m.s. (fig. 6) . The 

 principal migration was in the fall when flows at 

 the trapping site exceeded 1.5 c.m.s. As irrigation 

 was reduced at this time, most of the flow re- 

 mained in the stream dhannel, and water tempera- 

 tures ranged from 0° to 13° C. Winter migrations 

 were small and occurred only during short-term 

 increases in water temperature and flow. A sec- 

 ondary migration took place in the spring as water 

 temperature and flows again increased. The migra- 

 tion declined just before liigh flows from spring 

 rain and melting snow (fig. 6). Periodic sampling 

 during the high flows .suggested that few chinook 

 salmon were migrating. As water levels receded, 

 however, fish were taken in limited numbers imtil 

 the upstream diversion of water for irrigation 

 greatly reduced the flows at the louver. Water 

 temperatures increased in the spring from near 

 freezing to about 8° C. 



Chinook salmon of age-group O dominajted the 

 migration in the fall. These fish emerged from 

 the gravel in the spring and were the offspring of 

 adults that had spawned in late summer and early 

 fall of the previous year. The size of the 0-group 

 fish varied slightly from year to year and through- 

 out the migi'ation period (table 4). 



Juvenile chinook salmon that moved down- 

 stream from January into late spring were 

 primarily age-group I fish. A small number of age- 

 group (average, 60 mm.; range, 41-80 mm.) was 

 sampled from April through June 1963. Some age- 

 group II fish — less than 3 percent of the total 



Table 4. — Lengths of juvenile spring chinook salmon at beginning and end of spring and fall migrations at Eagle Creek, 196S-65 



